In recent years, methods for manufacturing electronic devices by ink-jet technology have received much attention. In response to electronic devices having higher densities, inkjet heads with higher densities have been demanded.
Stacked piezoelectric devices or thin piezoelectric devices are used for driving inkjet heads. Referring to FIGS. 19 to 21, an example of a piezoelectric device in Japanese Patent Laid-Open No. 9-174830 will be described below.
The piezoelectric device is configured for higher densities.
An inkjet head in FIGS. 19 and 20 includes a piezoelectric device unit 51 having a plurality of piezoelectric devices 50, a diaphragm 12 that has a plurality of vibratory projecting portions 10 for the piezoelectric devices 50 and transmits vibrations generated on the piezoelectric devices 50 through the vibratory projecting portions 10, and a nozzle plate 18 having a plurality of nozzle holes 14 formed thereon for the piezoelectric devices 50. Ink is injected from the nozzle holes 14 in response to vibrations transmitted from the piezoelectric devices 50 through the vibratory projecting portions 10.
The piezoelectric device 50 has dielectrics stacked in an X direction of FIG. 19. A voltage applied to the piezoelectric devices 50 in the X direction extends or shrinks the piezoelectric devices 50 in a Z direction, ejecting ink from the nozzle holes 14 in the Z direction. The nozzle holes 14 are staggered at different positions in the X direction in the nozzle plate 18.
FIG. 20 is a cross-sectional view taken along the line a-b of FIG. 19. A driving force from the piezoelectric devices 50 is transmitted to a passage 20 through the vibratory projecting portions 10, ejecting ink droplets Id from the nozzle holes 14 formed on the nozzle plate 18. A passage component 22 indicates an ink passage. A substrate 16 is composed of the passage component 22 and the nozzle plate 18.
FIG. 21 shows another piezoelectric device having different nozzle hole layout from FIG. 19.
As shown in FIG. 21, if ink droplets are simultaneously ejected from three nozzle holes 56 through vibratory projecting portions 52 and a diaphragm 54, a central passage 62 is deformed to a maximum level because of insufficient rigidity of a substrate 58 composed of a nozzle plate 60 and passage components 64. Hence, a volume reduction rate in the central passage 62 is smaller than that on both sides of the passage 62.
Thus, in the piezoelectric device of FIGS. 19 and 20, the nozzle holes 14 are staggered so as to suppress a volume reduction.